PROJECT SUMMARY/ABSTRACT Regular exercise promotes physical performance and health, and prevent various types of diseases. These benefits are largely mediated by responses and adaptations, particularly mitochondrial remodeling, in skeletal muscle. 5' AMP-activated protein kinase (AMPK) is a bioenergetics sensor that is critical for the maintenance of metabolic homoeostasis, and AMPK signaling has been linked to mitochondrial remodeling and functional adaptations under normal and disease conditions. However, the precise mechanism of AMPK signaling in control of mitochondrial remodeling with subcellular specificity remains obscure. We discovered a physical association of a novel AMPK complex (?1, ?2 and ?1 subunits) with mitochondria (referred to as mitoAMPK) in and unveiled its activation (T172 phosphorylation) under exercise and ischemic conditions. We have also obtained preliminary data to show that inhibition of mitoAMPK blocks exercise-induced mitophagy, a key step in mitochondrial quality control, in skeletal muscle. We now propose a completely novel hypothesis that mitoAMPK is preferentially activated at energetically stressed mitochondria during exercise, mediating precision mitophagy of dysfunctional or damaged mitochondria for functional and metabolic adaptations To test this hypothesis, we propose: 1) Determine if mitoAMPK is preferentially activated at energetically stressed mitochondria in skeletal muscle. 2) Elucidate the role of mitoAMPK in exercise-induced mitophagy. 3) Eetermine the functional role of mitoAMPK in exercise training-induced functional and metabolic adaptations. The proposed studies will capitalize on our novel findings of mitoAMPK that reveals completely new regulatory and functional features of this important signaling molecule in muscle biology and metabolism. The experimental design and model systems are both conceptually and technically innovative. The findings will significantly improve the mechanistic understanding of exercise-induced mitophagy and adaptations, with great potential impact on the future development of therapeutics for treatment and prevention ofchronic diseases, like type 2 diabetes.